Many sophisticated electronic circuits comprise a large number of fuses for protecting the circuitry and its power supplies against damaging short circuits and other excessive current drains. In such systems a single "blown" fuse usually means that the entire electronic device must be shut down until the defective fuse is found and replaced. This can require extensive time of skilled technicians and results in excessive down time of the hardware. The system of the present invention permits blown or open fuses to be quickly detected. The output of the system comprises a visual indictor which may comprise a light emitting diode (LED) which is connected to each one of the fuses of the system and is arranged to illuminate if its connected fuse fails or blows. A plurality of these on-line indicators may be connected to a master indicator which will indicate whether any one of the on-line indicators connected thereto has a defective fuse. This connection to the master indicator forms an OR gate. Such on-line indicators may be provided for all of the fuses or circuit breakers on an electronic sub-asssembly such as a circuit board, with all of the LEDs and associted circuits comprising these on-line indicators mounted on the circuit board. The aforementioned master indicator for all of the on-line indicators on a particular circuit board may then be located on the console or main control panel of the overall system. Thus illumination of the master fuse status indicator would indicate which of many circuit boards has the defective fuse and the technician would then simply inspect this board and its on-line indicators to quickly pinpoint the defective fuse and/or circuit.